In the operation of a drip or trickle irrigation system it is of prime importance that a small, yet uniform flow of water be delivered without danger of the system or parts of the system becoming permanently clogged by small particles of dirt or the like which are usually found in irrigation water.
U.S. Pat. No. 4,008,853, dated Feb. 22, 1977, discloses an emitter suitable for drip irrigation which provides both flow control and self-purging features. While the valve of this patent does provide desirable operational features it will be appreciated that it is somewhat difficult to mold in great quantities to exact tolerances.
U.S. Pat. No. 3,970,251, dated July 20, 1976, discloses an emitter valve design to provide constant flow rates under varying line pressure. Reference should also be had to several patents cited in U.S. Pat. No. 3,970,251, as representative of the state of the art in systems of this type.
U.S. Pat. No. 4,113,180, dated Sept. 12, 1978, discloses an emitter valve design having a longitudinal drip duct extending through the flow passage thereof. Application of fluid pressure causes the walls of the flow passage to collapse, limiting fluid flow through the valve solely to flow through the drip duct.